[OTA-1545] Extend ClusterVersion for accepted risks

- Add a new field 'clusterversion.spec.desiredUpdate.acceptRisks': It
  containsthe names of conditional update risks that are considered
  acceptable.
- Move `clusterversion.status.conditionalUpdates.risks` two levels up as
  `clusterversion.status.conditionalUpdateRisks`. It contains all the risks
  for `clusterversion.status.conditionalUpdates`.
- Add new field 'clusterversion.status.conditionalUpdates.riskNames': It
  contains the names of risk for the conditional update. It deprecates
  `clusterversion.status.conditionalUpdates.risks`.
- Add a new field 'clusterversion.status.conditionalUpdateRisks.conditions':
  It contains the observations of the conditional update risk's current
  status.

Author: hongkailiu